The delivery of drugs through the skin provides many advantages. Primarily, such a means of delivery is a comfortable, convenient and noninvasive way of administering drugs. The variable rates of absorption and metabolism encountered in oral treatment are avoided, and other inherent inconveniences—e.g., gastrointestinal irritation and the like—are eliminated as well. Transdermal drug delivery also makes possible a high degree of control over blood concentrations of any particular drug.
However, many drugs are not suitable for passive transdermal drug delivery because of their size, ionic charge characteristics and hydrophilicity. One method of overcoming this limitation in order to achieve transdermal administration of such drugs is the use of electrical current to actively transport drugs into the body through intact skin. The method of the present invention relates to such iontophoresis, which is an example of such an administration technique.
Herein the terms “electrotransport”, “iontophoresis”, and “iontophoretic” are used to refer to the delivery of pharmaceutically active agents through a body surface by means of an applied electromotive force to an agent-containing reservoir. The agent may be delivered by electromigration, electroporation, electroosmosis or any combination thereof. Electroosmosis has also been referred to as electrohydrokinesis, electroconvection, and electrically induced osmosis. In general, electroosmosis of a species into a tissue results from the migration of solvent in which the species is contained, as a result of the application of electromotive force to the therapeutic species reservoir, which results in solvent flow induced by electromigration of other ionic species.
During the electrotransport process, certain modifications or alterations of the skin may occur such as the formation of transiently existing pores in the skin, also referred to as “electroporation”. Any electrically assisted transport of species enhanced by modifications or alterations of the body surface (e.g., formation of pores in the skin) are also included in the term “electrotransport” as used herein. Thus, as used herein, the terms “electrotransport”, “iontophoresis” and “iontophoretic” refer to (a) the delivery of charged drugs or agents by electromigration, (b) the delivery of uncharged drugs or agents by the process of electroosmosis, (c) the delivery of charged or uncharged drugs by electroporation, (d) the delivery of charged drugs or agents by the combined processes of electromigration and electroosmosis, and/or (e) the delivery of a mixture of charged and uncharged drugs or agents by the combined processes of electromigration and electroosmosis.
Systems for delivering ionized drugs through the skin have been known for some time. British Patent Specification No. 410,009 (1934) describes an iontophoretic delivery device which overcame one of the disadvantages of the early devices, namely, the need to immobilize the patient near a source of electric current. The device was made by forming, from the electrodes and the material containing the drug to be delivered, a galvanic cell which itself produced the current necessary for iontophoretic delivery. This device allowed the patient to move around during drug delivery and thus required substantially less interference with the patient's daily activities than previous iontophoretic delivery systems.
In present day electrotransport devices, at least two electrodes are used simultaneously. Both of these electrodes are disposed so as to be in intimate electrical contact with some portion of the skin of the body. One electrode, called the active or donor electrode, is the electrode from which the drug is delivered into the body. The other electrode, called the counter or return electrode, serves to close the electrical circuit through the body. In conjunction with the patient's skin, the circuit is completed by connection of the electrodes to a source of electrical energy, e.g., a battery, and usually to circuitry capable of controlling current passing through the device. If the ionic substance to be driven into the body is positively charged, then the positive electrode (the anode) will be the active electrode and the negative electrode (the cathode) will serve as the counter electrode, completing the circuit. If the ionic substance to be delivered is negatively charged, then the cathodic electrode will be the active electrode and the anodic electrode will be the counter electrode.
Existing electrotransport devices additionally require a reservoir or source of the pharmaceutically active agent which is to be delivered or introduced into the body. Such drug reservoirs are connected to an electrode, i.e., an anode or a cathode, of the electrotransport device to provide a fixed or renewable source of one or more desired species or agents. A reservoir would include a reservoir matrix or gel which contains the agent and a reservoir housing which physically contains the reservoir matrix or gel. In addition to the drug reservoir, an electrolyte-containing counter reservoir is generally placed between the counter electrode and the body surface. Typically, the electrolyte within the counter reservoir is a buffered saline solution and does not contain a therapeutic agent. In early electrotransport devices, the donor and counter reservoirs were made of materials such as paper (e.g., filter paper), cotton wadding, fabrics and/or sponges which could easily absorb the drug-containing and electrolyte-containing solutions. In more recent years however the use of such reservoir matrix materials has given way to the use of hydrogels composed of natural or synthetic hydrophilic polymers. See for example, Webster, U.S. Pat. No. 4,383,529 and Venkatraman, U.S. Pat. No. 6,039,977. Such hydrophilic polymeric reservoirs are preferred from a number of standpoints, including the ease with which they can be manufactured, the uniform properties and characteristics of synthetic hydrophilic polymers, their ability to quickly absorb aqueous drug and electrolyte solutions, and the ease with which these materials can be handled during manufacturing. Such gel materials can be manufactured to have a solid, non-flowable characteristic. Thus, the reservoirs can be manufactured having a predetermined size and geometry.
Generally, the geometry of a reservoir can be described in terms of three parameters:                (1) the average cross-sectional area of the reservoir (“ARES”), defined as the arithmetic mean of reservoir cross-sectional areas measured at a number of different distances from and parallel to the body surface;        (2) the average thickness of the reservoir; and        (3) the body surface contact area (“ABODY”).        
References to reservoir housing configuration and the above parameters include not only the parameters of the physical reservoir housing, but also include the physical parameters of the reservoir gel or matrix as well.
Electrotransport drug delivery devices having a reusable controller designed to be used with more than one drug-containing unit have been described. The drug-containing unit can be disconnected from the controller when the drug becomes depleted and a fresh drug-containing unit can then be connected to the controller. The drug-containing unit includes the reservoir housing, the reservoir matrix, and associated physical and electrical elements which enable the unit to be removably connected, both mechanically and electrically to the controller. In this way, the relatively more expensive hardware components of the device (e.g., the batteries, the light-emitting diodes, the circuit hardware, etc.) can be contained in the reusable controller. The relatively less expensive donor reservoir and counter reservoir may be contained in the single use, disposable drug containing unit. See, Sage et al., U.S. Pat. No. 5,320,597; Sibalis, U.S. Pat. Nos. 5,358,483 and 5,135,479. Electrotransport devices having a reusable electronic controller with single use/disposable drug units have also been proposed for electrotransport systems comprised of a single controller adapted to be used with a plurality of different disposable drug units. For example, Johnson et al., WO 96/38198 discloses the use of such reusable electrotransport controllers which can be connected to drug units for delivering the same drug, but at different dosing levels, (e.g., a high dose drug unit and a low dose drug unit) which can be connected to the same electrotransport controller. Although these systems go far in reducing the overall cost of transdermal electrotransport drug delivery, further cost reductions are needed in order to make this mode of drug delivery more competitive with traditional delivery methods such as by disposable syringe.